How Do Lie Detectors Work

People talk about lie detectors all the time, you will hear them in movies, police investigations and when someone applying for some jobs. When someone applies to be a private investigator, and some government jobs (FBI or CIA) he or she would be required to take a polygraph test. The goal of the lie detector test is to check if the person being asked the questions is being honest or is lying about his or her responses.

Who Invented Polygraph Test?

The polygraph examination was first invent by John Larson in 1921. He was a medical student at University of California at Berkeley. From the beginning of the invention people were worried about how the invention works and how efficient the system is. There are people who have been known to lie at will and be able to beat the polygraph exam. In addition to there being good liars, there are also inept examiners who don’t know how to read whether a person is lying or not.

Four to six sensors are attached to the person who is taking the polygraph exam. A polygraph machine is used in the examination and it is one in which it reads multiple signals (poly) for the sensors and records on a single strip of moving paper (graph). The sensors record:

Breathing rate

Pulse

Blood pressure

Perspiration

Cases Which A Polygraph Record Arm And Leg Movement

There is a usually a pre-test before the actual polygraph test in which the questioner, a private investigator, asks three or four simple questions to find out the subject’s norms for his signals. Afterwards, the real questions being tested by the polygraph will be asked. Throughout the whole exam, the subject’s signals are recorded on the graph.

The polygraph examiner, a private investigator, will keep looking at the graphs during and after the tests to see whether the vital signs have changed significantly to the questions being asked. In most cases, serious changes like a faster heart rate, increased perspiration and higher blood pressure will show that the subject being asked questions is lying.

Why Polygraph Test Can Be Fooled?

A polygraph test can be fooled and is not perfect although when it used by a well-trained examiners, private investigator, he or she will be able to tell if a person is lying with a high level of accuracy. One should note that the examiners interpretation is subjective and people react differently to lying.

In conclusion polygraph works on a large percentage of the population. There are very few people who are able to beat the system. Over the years there has incredible steps in improving how the polygraph test works and anyone can use them to have the most accurate results. Many private investigators use these tools to get evidence.